test as well as the average results of the five most recent tests including
the current test. The Contractor may adopt limits for control coarser than
the specification limits for samples taken other than as delivered to the
mixer to allow for degradation during handling. When the amount passing
any sieve is outside the specification limits, the coarse aggregate shall
be immediately resampled and retested. If the second sample fails on any
sieve, that fact shall be reported to the Contracting Officer. Where two
consecutive averages of 5 tests are outside specification limits, the
operation shall be considered out of control and shall be reported to the
Contracting Officer. Concreting shall be stopped and immediate steps shall
be taken to correct the grading.
3.17.2
Quality of Aggregates
Thirty days prior to the start of concrete placement, the Contractor shall
perform all tests for aggregate quality required by ASTM C 33. In
addition, after the start of concrete placement, the Contractor shall
perform tests for aggregate quality at least every three months, and when
the source of aggregate or aggregate quality changes. Samples tested after
the start of concrete placement shall be taken immediately prior to
entering the concrete mixer.
3.17.3
Scales, Batching and Recording
The accuracy of the scales shall be checked by test weights prior to start
of concrete operations and at least once every three months. Such tests
shall also be made as directed whenever there are variations in properties
of the fresh concrete that could result from batching errors. Once a week
the accuracy of each batching and recording device shall be checked during
a weighing operation by noting and recording the required weight, recorded
weight, and the actual weight batched. At the same time, the Contractor
shall test and ensure that the devices for dispensing admixtures are
operating properly and accurately. When either the weighing accuracy or
batching accuracy does not comply with specification requirements, the
plant shall not be operated until necessary adjustments or repairs have
been made. Discrepancies in recording accuracies shall be corrected
immediately.
3.17.4
Batch-Plant Control
The measurement of concrete materials including cementitious materials,
each size of aggregate, water, and admixtures shall be continuously
controlled. The aggregate weights and amount of added water shall be
adjusted as necessary to compensate for free moisture in the aggregates.
The amount of air-entraining agent shall be adjusted to control air content
within specified limits. A report shall be prepared indicating type and
source of cement used, type and source of pozzolan or slag used, amount and
source of admixtures used, aggregate source, the required aggregate and
water weights per cubic meter cubic yard amount of water as free moisture
in each size of aggregate, and the batch aggregate and water weights per
cubic meter cubic yard for each class of concrete batched during each day's
plant operation.
3.17.5
Concrete Mixture
a.
Air Content Testing. Air content tests shall be made when test
specimens are fabricated. In addition, at least two tests for air
content shall be made on randomly selected batches of each
separate concrete mixture produced during each 8-hour period of
SECTION 03300A
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